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tapered aluminum pipe or tubing

I have an application in mind that requires some tapered tubing. Specifically, I need to be able to go from about 1 1/2 inches down to about 1/2 inch over a foot or so. Nothing about this is critical. It needs to be aluminum for heat transfer ability, and about .1 thick or so for ability to withstand pressure up to about 150 psi or so.

The closest starting point I can think of is an aluminum baseball bat. If I buy two bats and cut the tapered parts out, I'd have what I need, an inner part and an outer part that nest together.

Bats are fairly expensive though, so I'm looking for a better option. Any ideas?

0.1" might be a bit thick for spinning on a small machine, though it is aluminum. 150PSI probably only requires about 0.015" though mechanical stresses could affect that and you need some cross section for heat transfer, safety margins, etc.

Ok, here's what I'm up to now- for some time I've had the idea in my head that you could compress air more efficiently if you kept the heat out of it during the compression part of the cycle. So I figure that by compressing the air while having it in contact with as much surface area of heat sinking as possible, you could do that in large part.

The air trapped in the assembly I described is always spread thinly and in close contact with both inner and outer cones, so the heat produced from compression is absorbed very quickly into the aluminum. It can be blown away using a fan, or the assembly might be used as is since the whole thing is subject to the heat, and therefore would not heat to the same degree as say the head on a normal air compressor. That's the second benefit, that of more efficient pumping even when the pump has gotten hot.

What I'm thinking is that the effective stroke of the cylinder would be long compared to the effective diameter of the 'piston'. This in part means that the cycle time can be slower. In my example, I more or less suggested a cylinder diameter of 1.25 inches, so subtracting the area of the small end from the big end, the effective piston area becomes very close to 1 sq in., or in other words about 1.13 inches in diameter. I want to use a stroke of about 4 inches, and this brings up another idea- instead of a crankshaft, what's wrong with using a ballscrew and reversing a direct drive motor at the ends of the 'piston' stroke- a momentary interruption of power at each end would have the motor coming to a complete stop very quickly, so there's no braking to do, just electronic commutation to reverse the motor. Or another linear method of actuating the piston would be the three phase solenoidal type linear actuator.

As you can see, I'm wanting to try to create a compact and efficient compressor. Not for high CFM, but for low-use tools and almost 'back pocket' portability.

for some time I've had the idea in my head that you could compress air more efficiently if you kept the heat out of it during the compression part of the cycle. So I figure that by compressing the air while having it in contact with as much surface area of heat sinking as possible, you could do that in large part.

In a single stage compressor it will make no difference if the compression is adiabatic or isothermal.